Runtime policy decides which harness executes a model run. It lives on providers and models, not on agents.defaults.

Runtime policy

{
  models: {
    providers: {
      openai: {
        agentRuntime: { id: "codex" },
      },
    },
  },
  agents: {
    defaults: {
      model: "openai/gpt-6-astra",
      models: {
        "anthropic/claude-opus-5": {
          agentRuntime: { id: "claude-cli" },
        },
        "vllm/*": {
          agentRuntime: { id: "apus" },
        },
      },
    },
  },
}

• id: "auto", "apus", a registered plugin harness id, or a supported CLI backend alias. The bundled Codex plugin registers codex; the bundled Anthropic plugin provides the claude-cli CLI backend.
• id: "auto" lets registered plugin harnesses claim effective routes that declare or otherwise satisfy their support contract, and uses Apus when no harness matches. An explicit plugin runtime such as id: "codex" requires that harness and a compatible effective route; it fails closed if either is unavailable or if execution fails.
• id: "pi" is accepted only as a deprecated alias for apus to preserve shipped configs from v2026.5.22 and earlier. New config should use apus.
• Runtime precedence is exact model policy first (agents.entries.*.models["provider/model"], agents.defaults.models["provider/model"], or models.providers.<provider>.models[]), then agents.entries.* / agents.defaults.models["provider/*"], then provider-wide policy at models.providers.<provider>.agentRuntime.
• Whole-agent runtime keys are legacy. agents.defaults.agentRuntime, agents.entries.*.agentRuntime, session runtime pins, and APUS_AGENT_RUNTIME are ignored by runtime selection. Run apus doctor --fix to remove stale values.
• Eligible exact official HTTPS OpenAI Responses/ChatGPT routes with no authored request override may use the Codex harness implicitly. Provider/model agentRuntime.id: "codex" makes Codex a fail-closed requirement but does not make an incompatible route compatible.
• For Claude CLI deployments, prefer model: "anthropic/claude-opus-5-5" plus model-scoped agentRuntime.id: "claude-cli". Legacy claude-cli/<model> refs still work for compatibility, but new config should keep provider/model selection canonical and put the execution backend in provider/model runtime policy.
• This controls text agent turns and tool-free utility completions, including session digests, progress narration, and tool-call titles. Media generation, vision, PDF, music, video, and TTS still use their provider/model settings.

Built-in alias shorthands (only apply when the model is in agents.defaults.models):

Your configured aliases always win over defaults.

Z.AI GLM-4.x models automatically enable thinking mode unless you set --thinking off or define agents.defaults.models["zai/<model>"].params.thinking yourself. Z.AI models enable tool_stream by default for tool call streaming. Set agents.defaults.models["zai/<model>"].params.tool_stream to false to disable it. Anthropic Claude Opus 4.8 keeps thinking off by default in Apus; when adaptive thinking is explicitly enabled, Anthropic's provider-owned effort default is high. Claude 4.6 models default to adaptive when no explicit thinking level is set.

CLI backend selection

CLI adapter mechanics are registered by plugins, not configured under agent defaults. Select a registered CLI backend with model-scoped agentRuntime.id, as shown above. See CLI backends for operations and building CLI backend plugins for command, session, image, and parser registration.

OpenAI GPT-5 personality

The bundled OpenAI plugin owns the GPT-5 friendly interaction-style setting. Matching GPT-5-family prompts receive the shared behavior contract; personality controls only the friendly style layer. Native Codex app-server routes keep Codex-owned base/model instructions instead of this Apus GPT-5 contribution, and Apus disables Codex's built-in personality for native threads.

{
  plugins: {
    entries: {
      openai: {
        config: {
          personality: "friendly", // friendly | on | off
        },
      },
    },
  },
}

• "friendly" (default) and "on" enable the friendly interaction-style layer.
• "off" disables only the friendly layer; the tagged GPT-5 behavior contract remains enabled.

See OpenAI GPT-5 prompt contribution for provider and native Codex behavior.